The present invention relates to methods for the production of arylsulfides and to compositions made therefrom. In particular, the present invention relates to methods for the production of arylsulfides from the reaction of an aromatic compound with elemental sulfur in the presence of a solid acid catalyst, and to compositions made therefrom.
Arylsulfides are beneficial as lubricants, additives, solvents, and as intermediates to lubricant base stocks, drugs, and agricultural chemicals. A particularly desired arylsulfide is diphenlysulfide (DPS), a molecule with two benzene rings linked by a sulfur atom. DPS is a high-valued chemical that is used in the synthesis of alkylated diphenylsulfides (ADPSs), a family of high-performance synthetic hydrocarbon fluids useful in engine oil formulations. In addition, DPS is used as a starting material for the preparation of 4,4xe2x80x2-bis(chlorobenzene)sulfone, a monomer used in the production of high-performance thermoplastic polysulfones.
DPS can be prepared from benzene, sulfur monochloride, and aluminum chloride according to the following reaction scheme: 
Other routes for the large scale production of DPS have been described. For example, synthetic routes for the production of DPS have been described which use the high-temperature thermal reaction of chlorobenzene with hydrogen sulfide or the reaction of benzene with sulfur using stoichiometric amounts of AlCl3 or zeolites in a batch-type reactor.
In addition, the production of DPS via an acid-catalyzed reaction between benzene and sulfur was first reported by Friedel and Crafts. The reaction is believed to proceed through an aromatic electrophilic substitution mechanism. The acid catalyst enhances the electrophilicity of sulfur via the formation of positively charged sulfur intermediates. These intermediates are believed to be produced by the formation of a Lewis acid-base adduct between sulfur and the Lewis acid or by the protonation of sulfur by a Bronsted acid. Products of the reaction include DPS, thiophenol, diphenyldisulfide (DPDS), thianthrene (TT), and phenylenesulfide oligomers and polymers, with the distribution of products depending strongly on the molar ratio of benzene and sulfur.
However, none of the known routes provide an adequate commercial source of DPS. Rather, the known processes suffer from numerous drawbacks, including, for example, the use of corrosive reactants (e.g., halogenated hydrocarbons), the production of corrosive by-products (e.g., gaseous hydrochloric acid), poor selectivity (e.g., the production of significant amounts of phenylenesulfides and chlorinated compounds, such as chlorobenzene), the need for extensive downstream separations (e.g., separation of catalyst from the product stream), and the generation of large amounts of benzene-containing catalyst waste. Similar problems have been encountered in the production of other phenyl sulfides, such as the thianthrenes.
These drawbacks have negative implications for the commercial use of ADPSs. The commercial use of ADPSs has been hampered by the need to purify the DPS prior to use as a reactant in the formation of the ADPSs. In particular, the poor selectivity for DPS and the presence of high concentrations of corrosive by-products made it imperative that the DPS be removed from the product stream prior to use. However, the purification of the DPS is expensive and time consuming.
In light of the foregoing, the large scale production of DPS has been expensive. Further, the high cost of producing the starting material DPS has prevented the ADPSs from being commercialized.
Accordingly, it would be highly beneficial to provide a method for the large scale production of arylsulfides. The method should provide for the production of arylsulfides in large yield without the use of highly corrosive reactants. Further, the method should produce little or no corrosive and/or undesired by-products. In addition, the method should utilize readily available reactants and be selective.
The drawbacks associated with the known methods for producing arylsulfides is overcome, to a large extent, by methods in accordance with the present invention. The present invention provides a method for producing arylsulfides wherein an aromatic compound and sulfur are reacted in the presence of an acidic catalyst. The reaction is very clean and produces little undesirable by-products. Usually, high sulfur conversion and selectivity to arylsulfides can be obtained under mild reaction conditions. The method can be used to produce arylsulfides in large scale and at economical prices.
In one of its aspects, the present invention relates to methods for the production of arylsulfides wherein an aromatic compound is reacted with elemental sulfur in the presence of a solid acid/oxide catalyst. The aromatic compound can be alkylated. In a preferred embodiment, the acid catalyst is a molecular sieve, preferably a zeolite such as MCM-56, ZSM-5, MCM-22, MCM-68, and USY. The reaction is optionally performed in a fixed-bed reactor.
In another of its aspects, the present invention relates to methods for the production of alkylated diphenylsulfides wherein an alkylated aromatic compound is reacted with elemental sulfur in the presence of a solid acid catalyst. In a preferred embodiment, the acid catalyst is a zeolite, such as MCM-56, ZSM-5, MCM-22, MCM-68, and USY. The reaction is optionally performed in a fixed-bed reactor.
In yet another of its aspects, the present invention relates to methods for the production of alkylated diphenylsulfides wherein an aromatic compound is reacted with elemental sulfur and an alkylating agent in the presence of a solid acid catalyst. The alkylating agent is preferably an olefin, more preferably a C6 to C20 olefin, and most preferably a C10, to C8 alpha olefin such as dodecene-1, decene-1, and tetradecene-1. In a preferred embodiment, the acid catalyst is a zeolite, such as MCM-56, ZSM-5, MCM-22, MCM-68, and USY.
Additional features and embodiments of the present invention will become apparent to those skilled in the art in view of the ensuing disclosure and appended claims.